CARTILAGES. 7 



the animal is irritated, and give it a rather ferocious appearance. 

 These beards are disposed in symmetrical patterns, upon the 

 dorsal surface, and particularly around the eyes, and their nuin- 

 ' ber and position form available distinctive characters. 



It will be readily understood, from the above, that color is 

 scarcely characteristic of species in. the cephalopoda, and that 

 care is necessary to separate these surface elevations, which may 

 be considered permanent from such as are due to the will of the 

 animal. The littoral species of Octopus, etc., which ordinarily 

 await their prey, instead of pursuing it like the finned pelagic 

 species, seem to possess and exercise, to some extent, a power of 

 color mimicry, in preventing their victims from distinguishing 

 them from circumjacent objects. 



Cartila</e* (Plate 1). 



The cartilaginous supports of the principal nerve-ganglia 1 are 

 well-developed, sometimes completely enveloping them; besides 

 which the principal organs of sense, the valves of the mantle, the 

 lins, etc., are duly provided. 



As might be expected from its habits, the cartilaginous system 

 of the Nautilus is the most simple of all the cephalopods, con- 

 sisting of a well-developed head-cartilage, so shaped and situated 

 as to support the oesophageal ring, the cerebnd mid pedal com- 

 missures, whilst two prolongations of it serve the funnel or 

 siphon. 



In the dibranchiata, unlike the Nautilus, the head-cartilage 

 forms a complete ring around the (esophagus: from the medial 

 line of the back of this ring spring two lancet-form cartilaginous 

 processes, the cartilages of the eyelid, and the under side of the 

 same ring spreads into a spoon-shaped process which comes far 

 forward and supports the eyes ; particularly when, as in Sepia, 

 it reaches to the sides of the head and encompasses the ocular 

 opening. 



The cartilages of the back and of the lins are shown in position 

 in Plate 1, fig. 1, after Keferstein, of Sepia, ufficihdlis. In the 

 Loligos the moon-shaped cartilage of the back is wanting, but is 

 replaced in its functions by the upper end of the corneous pen 

 or inner shell. In the Octopods there remains only of this back- 



